The present invention relates to electric motor powered, cam driven fastening tools. More particularly, the present invention relates to cam driven electric staplers.
Conventional electric staplers contain various features in an attempt to provide the user with an easier-to-use, quieter, more reliable stapler. These staplers, however, still do not adequately solve the noise, cost, and operational reliability limitations inherent in using numerous reducing and driving gears and multiple separate cam mechanisms to convert motor rotation into operational functions and in using bulky coil spring assemblies to prevent motor binding due to the insertion of relatively thick stacks of paper.
For example, U.S. Pat. No. 5,460,313 discloses a stapler with a motor mounted in the base and having a worm gear to drive a plurality of transversely mounted gears. A pair of arms to drive the staples are mounted transverse to the plurality of gears and are reciprocated by annular cam curves on the gears, cam wheels, and a specially shaped hole on a locking plate. The locking plate is also provided with an arcuate slot to compensate for varying thicknesses of paper to be stapled. The stapler disclosed is a relatively complicated structure using transversely mounted gears, cams, and arms that would likely contribute to operational noise and are subject to less reliable operation.
U.S. Pat. No. 2,770,805 discloses a stapling machine having two pairs of cams, drive cams and control cams. The drive cams rotate in contact with cam rollers disposed on a shaft to drive two separate sets of beams. The cam rollers lift a set of beams and the anvil and pivots the second pair of beams to depress the staple driver. A coil spring assembly attached to the pivoting beams driving the staples the accommodate varying thicknesses of paper and a spring urges the staple driver and the anvil apart. The control cams directly activate contact arms to control the input of power to the motor. This arrangement contains numerous moving parts that pivot along different axes and as such is more costly and less reliable.
Thus, there remains a need for improvements in these types of devices, and the present invention provides these.
In accordance with the present invention, applicants have developed a more reliable and simpler electric stapler that is less costly and easier to manufacture. The stapler includes a housing or frame and a head assembly pivotally disposed in the frame between a first open position and a second clamped position. The head assembly contains all of the operative elements of the stapler necessary to staple a stack of papers and is biased-toward the open position by a biasing member disposed between the head assembly and the frame.
The operative elements include a staple driving and forming mechanism reciprocally disposed in the head assembly between an up starting position and a down driving position, a motor fixed to the head assembly, and a single, multi-functional cam member connected to the motor and rotated thereby. Upon rotation, the cam member simultaneously forms and drives staples, pivots the head assembly in the frame, and actuates a microswitch controlling power to the motor. In addition, the cam member can drive a flat clinch mechanism.
In order to provide these four functions, the cam member includes a first cam surface to actuate a microswitch, a second cam surface connected to the staple driving mechanism to reciprocate the mechanism, a third cam surface to engage a first bar fixed to the frame to pivot the head assembly, and a fourth cam surface to engage a second bar also fixed to the frame to drive the flat clinch mechanism. The first bar is disposed between the frame and a spring assembly to permit the first bar to flex away from the frame to accommodate varying thicknesses or amounts of paper to be stapled. Fewer operative parts are need, because the motor and cam member surfaces all rotate around parallel axes that are perpendicular to the axes about which the head assembly pivots.